In a wireless LAN of IEEE802.11a/g, terminals in a network share one channel having a 20-MHz bandwidth to communicate with each other. In IEEE802.11n which has been currently standardized, a frequency band (channel) to be used is expanded to attain speeding up.
As a speeding up method, a method of making communications using two neighboring channels, i.e., a 40-MHz bandwidth has been examined. In IEEE802.11n, one of two channels is handled as a main operation channel (master channel) and the other channel is handled as an expansion channel (slave channel). A beacon signal as a reference signal is sent using the master channel.
Japanese Patent Laid-Open No. 2000-022712 discloses a configuration which selects a channel to be used in a wireless communication system that makes communications using one channel.
However, when a frequency band (channel) is expanded without careful consideration, communications of other apparatuses may be disturbed. For example, upon expanding the frequency band, communications of an existing wireless network may be disturbed. An apparatus which belongs to an identical network before expansion of the frequency band may no longer be able to make a communication after expansion of the frequency band.